Deep eutectic solvents (DES) based on a Hydrogen Bond Acceptor (HBA) generally a quaternary ammonium and a Hydrogen Bond Donor (HBD) of very diverse chemical natures, have been presented since 2003 as cheap, easy to prepare and biodegradable solvents. They are interesting alternative to ionic liquids or organic solvents and were employed in this project to extract bioactive polar compounds from wheat bran in comparison to classic organic solvents. The objectives of the work was to determine the potential of DES to extract antioxidant compounds from wheat bran and characterize these DES extracts in terms of composition and reducing power.
Soft Wheat bran (Bermude variety) was cryoground before being extracted with seven DES based on cholinium chloride or betaine as HBA in comparison with three organic solvents (acetone/water 50:50 v/v, n-propanol/water 70:30 v/v or ethanol/water 60:40 v/v). The contents in phenolic acids (gallic, vanillic, ferulic, sinapic, coumaric) and hexyl resorcinol in the extracts were determined by UV-HPLC. Putative identity of other compounds was studied by mass spectrometry (Esi-Ms/Ms). Reductive power of the extracts were assessed by DPPH radical scavenging capacity assay.
The best organic solvent acetone/water 50:50 v/v allowed extracting ~13 mg/100 g phenolic acids among which 3.4 mg/100 g ferulic acid. This quantity was 1.6 fold enhanced using cholinium chloride/lactic acid DES 1:10. Glycosylated flavonoids were also detected by mass spectrometry in this extract. The reductive power of this DES extract was also the strongest among DES and more important than Trolox at 1 µM. An insight into the tensioactive properties of this DES indicated that it was strongly tensioactive (22 mN/m at 0.5 % in phosphate buffer), property which could contribute to its high extractive power.
DES could constitute good media to concentrate wheat bran antioxidants and add value to this abundant low-cost by-product of the milling industry.